The evolution of packet-based communications has lead to providing telephony services and features over packet subsystems in addition to circuit-switched subsystems. These packet subsystems were initially supported by local area networks, but are now supported by wireless local area networks and cellular networks. Cellular networks support access to both circuit-switched and packet subsystems through available cellular access networks.
Unfortunately, the circuit-switched subsystems and the packet subsystems are substantially independent. Given the existing infrastructure, most call control and feature support is provided in the circuit subsystem. Various multimedia subsystems, such as the Third Generation Partnership Project (3GPP) Internet Protocol (IP) Multimedia Subsystem (IMS), are separate from, but associated with, the packet subsystem and have evolved to support packet-based services and features for the packet subsystems. The IMS is evolving to provide only basic interaction with the circuit-switched subsystem and is optimized for Session Initiation Protocol (SIP) based services. As such, IMS has limited influence or control over the circuit-switched subsystem.
In certain IMS configurations, packet-based services for a mobile terminal are interrupted when the mobile terminal is involved in a circuit-switched call. Further, there is often limited capacity to support voice applications using voice over IP (VoIP) in the packet subsystem. In other IMS configurations, the IMS can interact with the circuit-switched subsystem when establishing calls as well as support VoIP in the packet subsystems. However, once a call is established in the circuit-switched subsystem, the IMS loses control of the call and therefore cannot provided additional services associated with the call in the circuit-switched subsystem. The inability to provide overall control of the circuit-switched and packet subsystems in an orchestrated and comprehensive manner limits the availability of services and features to telephony users, especially those with mobile terminals that support communications over both the circuit-switched and packet subsystems.
As such, there is a need for a technique for providing effective and efficient control over both circuit-switched subsystems and packets subsystem to enable unfettered support of services and features to users via mobile terminals.